Definitely time for a tube change. Stop turning it on until you change the tubes, or you might damage something.

My DT25 head has started blowing the tube protection fuse.
This happens shortly after i turn it on.

I have noticed the following before it happens:
1. I turn on the amp.
2. wait for a minute or two.
3. The amp starts making crackeling noice and one of the power tubes starts glowing brightly (like it has a hot spot all orange)

I have two DT25's and have experienced the same problem on both amps...

The amp starts making crackling noise and one of the power tubes starts glowing brightly (like it has a hot spot all orange)

I replaced the power tubes on one amp and it seemed to work ok, but after a short time I get an annoying tone happening (Like feedback (Kind of a sine-tone), but the sound is there even when the guitar is not plugged in - although not very loud, just loud enough to be VERY annoying). This tone comes and goes, usually takes about 10 minutes after the amp is turned on before the noise appears. If I turn off the amp, and then on again after a short while (While the amp is still warm) the noise usually reappears instantly.

My other DT25 has turned completely silent (I have tried replacing the power-tubes to no avail). It might possibly be a software problem, because when I turn on the power, all the lights go on (Like the initial power-up sequence), but there is no response from any of the knobs - Everything is "frozen" and the amp is dead-silent. I can see that there is power on the tubes, because they are all glowing, so the power seems to be ok.

Both of my amps are early production-models (First one was bought in november 2011 and the second one in september 2012) and someone told me that there has been issues with some of the early production-models. Does anybody know anything about this?

I really like the sound in the DT25, but now I'm stuck with TWO amps that are not working :-( (And no warranty either....)